The U.S. Supreme Court building in Washington, D.C.Mark Wilson/Getty Images

The U.S. Supreme Court has agreed to hear a new challenge to a key provision of President Barack Obama’s health care law, the Associated Press reports. The challenge threatens to curb subsidies that help millions of low- and middle-income people afford health insurance premiums.

The justices on Friday agreed to review a federal appeals court ruling that upheld IRS regulations that allow health insurance tax credits under the Affordable Care Act for consumers in all 50 states, the report says. Opponents contend that most of the subsidies are illegal.

It will be the second time an important aspect of the law has been scrutinized by the Supreme Court in the protracted battle by opponents of the ACA to overturn or limit the historic 2010 health insurance measure. The court upheld the heart of the law in 2012, with conservative Chief Justice John G. Roberts Jr. providing the critical vote.

White House press secretary Josh Earnest vowed a vigorous defense before the high court, AP reports. The case is likely to be argued in the first week of March, with a decision expected by late June.

“This lawsuit reflects just another partisan attempt to undermine the Affordable Care Act and to strip millions of American families of tax credits that Congress intended for them to have,” Earnest said, according to AP.